A statistical parameter or population parameter is an amount put into the probability distribution of a statistic or a random variable. It can be thought of as a numbered amount of a trait of a statistical population or a statistical model.
A statistical parameter is different from its estimator in that the parameter is a fixed amount, while the value of an estimator changes according to some probability distribution. The notations (for the parameter) and (for the estimator) are often used to clarify this distinction.
